On aircraft there are numerous ducts to handle the flow of air from the engine to various air systems such as the airconditioner or the thermal anti-icing system. The space is limited and the ducts must be flexible so ball joints are used to obtain the flexibility. These ducts operate at temperatures from ambient up to about 940.degree. F. and operate under pressures from atmospheric to 8 psi. when the engine is at idle and up to about 600 psi. at takeoff. In addition to this the ducts are subjected to considerable vibration. Due to these conditions, the ball joint is sealed with a metal wear ring. The old style metal wear ring has a spherical surface on each side to match the closure surfaces on nut and flange. The wear ring, being spherical and of a consistant thickness, is not compressible and is incapable of compensating for variations in the mating nut and flange due to distortions caused by normal fabrication and assembly requirements. The only past method for reducing leakage was by excessive tightening of the nut and flange which defeated the flexibility requirement and, if truly excessive, could cause premature fatigue failure on the duct. Generally the joint would "wear-in" in service and reduce leakage instead of becoming worse. When a wear ring must be replaced it takes considerable time to disassemble to get to the leaking ball joint and the wear ring must be split to permit removal of the faulty ring and to permit the installation of a new ring.
A metal wear ring was discovered that prevents leaks in the air duct ball joints.